1. Field of the Invention
The present invention relates generally to materials handling apparatus used in manufacturing, and, more particularly, to devices for automatically accessing disk-shaped objects present in a carrier.
2. Description of the Prior Art
Recently, semiconductor equipment manufacturing companies have adopted a new standard for sealed carriers to be used for transporting 300 mm diameter, disk-shaped, semiconductor wafers between semiconductor processing machines. This new standard carrier, identified by the name Front Opening Unified Pod ("FOUP"), differs from a prior carrier for 8 inch diameter, disk-shaped, semiconductor wafers, identified by the name Standard Mechanical InterFace ("SMIF"), in various different ways. For example, exposing 8 inch diameter semiconductor wafers that are enclosed within the prior SMIF pod requires unlatching and removing from a base of the SMIF pod a one-piece removable cover that provides the top and sides of the SMIF pod. Alternatively, gaining access to 300 mm diameter semiconductor wafers enclosed within the newer FOUP requires unlatching and removing a door from one side of the FOUP.
Furthermore, while the prior SMIF pod has only one size, the recently adopted standard actually envisions four different sizes of FOUPS. First, the standard envisions FOUPs that are capable of carrying, in uniformly-spaced slots located within the FOUP, either 13 or 25 semiconductor wafers. These two different classes of FOUPs are respectively identified herein by the phrases shorter FOUP and taller FOUP. Second, the standard also envisions FOUPs identified as unified or non-unified. A non-unified FOUP encloses a separately removable wafer boat that, depending upon the carrying capacity of the FOUP, holds either 13 or 25 semiconductor wafers in its uniformly-spaced slots. Conversely, a unified FOUP omits the separately removable wafer boat. Thus, in general, a unified FOUP allows removing only a single wafer at a time from the FOUP's uniformly-spaced slots, or inserting only a single wafer at a time into one of the FOUP's slots. Conversely, a non-unified FOUP allows simultaneously removing from the FOUP, en masse, as many as 13 or 25 semiconductor wafers that are held within the wafer boat, or simultaneously inserting into the FOUP, en masse, as many as 13 or 25 semiconductor wafers that are held within the wafer boat. Because the non-unified FOUP must enclose the separate, removable wafer boat, the non-unified FOUP has a larger exterior than the smaller non-unified FOUP capable of carrying an identical number of semiconductor wafers. Correspondingly, the recently adopted standard envisions four different sizes for the door on the side of the FOUP that must be removed to gain access to 300 mm diameter semiconductor wafers enclosed within the FOUP.
To permit mechanically clamping a FOUP to semiconductor processing equipment, each FOUP includes both wedge shaped ramps on the exterior of the FOUP, and oval shaped holes in the bottom of the FOUP. Because semiconductor manufacturing requires extreme cleanliness, semiconductor processing equipment must include a load port interface that automatically unlatches and removes the door from the side of the FOUP secured thereto to expose to the wafer processing equipment the semiconductor wafers enclosed therein. After semiconductor wafers have been processed, the semiconductor processing equipment must also automatically reinsert and relatch the door onto the side of the FOUP to seal the wafers within the FOUP. One existing load port interface adapted for opening and closing a FOUP employs a pivoting arm one end of which carries an end-effector adapted to mate with and engage the FOUP's door. After the end-effector engages and unlatches the FOUP's door, the arm rotates away from the FOUP swinging the end-effector carrying the door through an arc thereby exposing the semiconductor wafers within the FOUP. Conversely, the arm of such a load port interface rotates toward the FOUP to swing a door carried by the end-effector into a latching position on the side of the FOUP where the end-effector the subsequently relatches the door onto the FOUP.
While depending upon the type of FOUP, FOUPs may carry either 13 or 25 wafers, they may also carry a fewer number of wafers in the uniformly-spaced slots provided by the unified FOUP, or by the wafer boat included in the non-unified FOUP. Thus, effective utilization of semiconductor processing equipment requires that such equipment determine the number and location of semiconductor wafers within a FOUP after the FOUP has been opened before the equipment begins processing those semiconductor wafers. Moreover, while the specification for and design of the FOUP envisions only carrying a single wafer in each of the uniformly spaced wafer slots, during real-world operation of automatic wafer handling equipment sometimes:
1. two (2) wafers may, in fact, be inserted into a single slot; or PA1 2. a single wafer may be inserted at a skewed angle so diametrically opposite edges of the wafer are respectively located in two (2) immediately adjacent slots. PA1 a) a single semiconductor wafer occupies a particular slot in the FOUP; PA1 b) a semiconductor wafer crosses a slot within the FOUP thereby the semiconductor wafer has a segment of the edge thereof disposed in a first slot and a diametrically opposite segment of the edge thereof disposed in a second slot that is immediately adjacent to the first slot; and PA1 c) a single slot holds two semiconductor wafers.